Conventional impact crushers include a crushing chamber and a rotor mounted for rotation in the crushing chamber, the rotor being configured for striking feed material present in the crushing chamber. The rotor typically includes a plurality of arms, often referred to as ‘hammers’ or ‘blow bars’, which serve as primary impact devices for breaking down feed material in the crushing chamber.
Known impact crushers include a body within the crushing chamber, often referred to as an ‘apron’ or ‘anvil’, having an impact surface against which material present within the chamber may be comminuted during operation of the rotor. The impact surface of the apron may be arranged at a predetermined distance from the swept area of the rotor, in order to control the maximum grade of material that can pass through the crushing chamber.
An example of a known impact crusher of the kind set forth above is shown in U.S. Pat. No. 6,745,966, in which aprons are pivotably mounted within the crushing chamber. Each apron is coupled to an hydraulic cylinder or threaded spindle arrangement, which is used to set the spacing between the impact surface of the apron and the swept area of the rotor.
It will be understood that the apron is subjected to forces during comminution of material against its impact surface. Typically, the apron may be spring-loaded to provide a reaction against said forces. However, uncrushable oversize material in the crushing chamber may result in the generation of forces which exceed the spring-load, causing the apron to move away from the rotor, until said material has passed beyond the apron. The spring-load will then return the apron to its normal working position.
In a known crusher, the working position of the apron relative to the rotor is set using an hydraulic cylinder arrangement. This arrangement is also used to reset the working position of the apron, after passage of an uncrushable object, wherein a proximity sensor is used to detect when the apron has reached the desired working position.